DE3033109A1 - METHOD FOR PRODUCING PHOSPHOROXIDE OXIDE USING THE REACTION HEAT - Google Patents

Abstract

The invention relates to process for making phosphorus pentoxide by subjecting elementary phosphorus to a combustion reaction with the aid of air, the reaction heat being utilized for the production of energy. To this end, the invention provides for the phosphorus to be subjected to combustion with dry air containing, per m3, 5 g down to 0.01 g of water, inside a combustion chamber of which the metallic walls are arranged so as to form a cooling system with cavities therein and for a liquid and liquid/steam-mixture, respectively, to be circulated through the cooling system under pressure within the range 1 to 150 bars, the liquid or mixture assuming a temperature of more than 150 DEG C. up to 500 DEG C. Steam which is formed in the cooling system is continuously taken therefrom and replaced by an equivalent proportion of fresh liquid.

Description

The invention relates to a method for producing phosphorus pentoxide by burning elemental phosphorus • with the help of air using the heat of reaction to generate energy.

It is known from DE-PS 1 300 527 to produce phosphorus pentoxide and polyphosphoric acid by oxidation of yellow phosphorus and absorption of PpOj- .in polyphosphoric acid, whereby for the simultaneous production of solid, hexagonal PpOc and polyphosphoric acid in a first reaction zone, their Walls are cooled to temperatures below 150 ° C, preferably below 100 ° C, melted, elemental phosphorus burns with a molecular oxygen-containing gas in the upper part of the reaction zone, part of the gaseous P ₂ O ₅ condenses in the reaction zone, the solid P ₂ Oe from the lower part of the. The reaction zone discharges and the exhaust gases leaving the reaction zone and containing not separated P ₂ ⁰ K are fed to a second reaction zone in which, for the production of polyphosphoric acid, a polyphosphoric acid which has a lower content of P ₂ O ₅ than contains the desired polyphosphoric acid as the end product, circulates and therein that in the exhaust gases of the first ^:

Reaction zone contained P _o 0 _c absorbed.

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_COpY . ORiGiMAL INSPECTED

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The above-described process of burning yellow phosphorus in the presence of excess air is known strongly exothermic, with an amount of heat of 5813 Kcal, corresponding to 24 233 KJ per kg of phosphorus burned free. 5 is set, which is achieved by intensive cooling of the walls of the combustion chamber to temperatures below 100 ° C must be removed as quickly as possible. A particular difficulty lies in choosing the right material for the combustion chamber, in which the phosphorus.

oxidation is carried out.,. The high flame temperature, the presence of oxygen, the high aggressiveness of both the hot phosphorus pentoxide vapors and the Phosphoric acid mist, the oxide from the phosphorus and the water vapor contained in "the air or oxygen will cause very severe corrosion on the inner wall of the combustion chamber. The corrosion problem is understandably more serious, the higher the cooling temperature in the cooling elements of the Combustion chamber is selected. In this respect, it has not been possible until now to reduce the incineration of yellow phosphorus To supply the heat of reaction occurring in excess air to a further technical use, rather the resulting amounts of heat had to be dissipated uselessly using considerable amounts of cooling water.

The problem of recovering and utilizing the • The heat of reaction arising from the combustion of yellow phosphorus with air is already mentioned in the literature discussed by A.D .. Mikhailin et al. in "The Soviet Chemical Industry 5", No. 7, July 1973, and reference is made to the risk of corrosion of the materials exposed to the combustion process. Even high-quality special nickel-based stainless steels were recognized as unsuitable in the long term. ·

QOPY ORIGINAL INSPECTED

It has now been found that the production of Phos -—-'- - phosphorus pentoxide by burning yellow phosphorus with air with recovery of the heat of reaction and under Overcoming known corrosion problems can be operated without difficulty if one uses the method performs under certain conditions.

The invention thus provides a method for ^: Production of elemental phosphorus with the aid of air under. Utilization of the heat of reaction to generate energy, which is characterized in that the phosphorus combustion is carried out with dried air with a water content of 5 to 0.01 g / nr air in a combustion chamber, the metal walls of which form a cooling system which expands into cavities are formed, wherein a liquid suitable as a heat carrier for the heat of reaction or a liquid-vapor mixture is circulated in the cooling system while being heated to temperatures of over 150-500 ° C. at pressures of 1-150 bar; that the vapor generated in the cooling system is continuously withdrawn from the latter and replaced by an equivalent amount of fresh liquid, and that the hot PpOc vapors escaping from the combustion chamber are condensed or processed into secondary products. 25th

The pre-dried air used to burn the phosphorus preferably has a water content of

• 0.3 to 0.1 g / m ³ air.

Furthermore, "it has proven to be advantageous as a heat transfer medium or using the circulating liquid water. The circulating liquid or the The heat absorption generally increases the liquid-vapor mixture to temperatures of 200 to 400 ° C. at pressures heated from 15 to 90 bar.

COPY ORIGINAL INSPECTED

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To avoid corrosion it is recommended that the Manufacture walls or the cooling system of the combustion chamber from stainless steel according to DIN 17 440. the Walls of the combustion chamber can, for example, be made of a metallic pipe wall directly welded to it Tubes or a fin tube wall or a membrane tube wall exist.

The phos- " Phosphorus pentoxide vapors usually leave the combustion chamber at a temperature of 300 to 1000 ° C. They can either be condensed or processed into phosphoric acid.

.15 Two exemplary embodiments of devices which can be used for carrying out the method of the invention have proven themselves are shown in the drawing as FIGS. 1 and 2.

Figure 1 shows essentially the combustion chamber for. Burning of the yellow phosphorus, which comes from the protective jacket with insulation (1) for the metallic pipe wall (2) consists, with the individual tubes arranged vertically. The combustion chamber is also equipped with a device

(3) to atomize the yellow phosphorus with air. equips, the air via the line (4) and 'the previously liquefied phosphorus are supplied via the line (5). Inside the combustion chamber there is a partition made of pipes (6) to divert the combustion gases or the phosphorus pentoxide vapors, which are drawn off via the opening (7) and line (8). To accommodate the The individual tubes of the tube wall (2) carry heat of combustion, for example water, which partially evaporates. the Separation of steam and water takes place in the separator (9), the steam being drawn off via line (10).

GOPY

Non-evaporated water returns in via line (11) 'back the pipe wall (2). ■ occurred through evaporation Water losses are supplemented by supplying fresh water via line (12) with feed pump (13). 5

The device according to FIG. 2 differs from the device according to FIG. 1 only in that the individual pipes of the pipe wall (2) are mounted horizontally. · ^: "-. is effected.

The technical progressiveness of the inventive ' The procedure is unmistakable, as there is currently no possibility of using the resulting from the implementation of the procedure Heat of reaction gave. Prejudices regarding the sufficient resistance of the materials of the device maintained at the cooling temperatures in the combustion chamber of over 100 ° C required for steam formation the person skilled in the art from getting closer to solving the problem according to the invention. After surprisingly no deposit formation under the process conditions of the invention occurs on the pipes of the pipe wall and thus ■ a good transfer of the heat of reaction to the liquid Heat transfer medium, e.g. B. water, is guaranteed, and on the other hand, corrosion of the material of the combustion chamber. because of the use of pre-dried air does not occur to the expected extent, the "invention has a feasible one Way to the production of phosphorus pentoxide with simultaneous economic use of previously unused Energy.

The method according to the invention is carried out by the following Examples explained in more detail.

COPY,;

Example Ί

In a combustion chamber with pipe walls (2) made of stainless steel, 100 liters or 170 kg of elementary, liquid, yellow phosphorus were burned per hour at a temperature of 75 ° C. in the presence of dry air at a pressure of 6 bar. The heat of reaction of 4 GJ / h released during combustion became 50%. through the pipe. . walls are transferred to the heat transfer fluid in the form of fully demineralized and degassed water. Partial evaporation of the water occurred. ·

The water / steam mixture rose through the individual pipes (2) into a collecting pipe and then into the vapor separator. (9), in which a separation of vapor and liquid takes place. * found. The vapor pressure in the separator was determined by a pressure

control valve in line (10) kept at 20 bar and . _ the generated saturated steam in an amount of 1.1 t per hour withdrawn via the line (10). The liquid phase in the separator (9) was via the circulation line (11) and a lower one Distributor pipe fed to the riser pipes in the pipe wall (2). With that the circle of the liquid circulation was effected closed by the density differences in the circulation system.

By means of a "level control" attached to the separator (9) it was ensured that the cooling system was always supplied with sufficient water, with fresh water additives over the line (13) took place. The burner (3) was placed down in the combustion chamber, creating the section radiant heat was applied to the chamber near the burner. In this part were wall temperatures measured between 300 and 400 ° C. The combustion gases were deflected in the lower area of the combustion chamber by 180 °, so that Phosphorpentoxiddäm could leave via the trigger (7).

35 · by 180 ° so that phosphorus pentoxide vapors enter the combustion chamber

COPY ORiGfNAL INSPECTED

Example 2

The procedure was as in Example 1, except that the tubes of the combustion chamber were partially horizontal or were arranged only slightly rising. In addition, the circulation of the heat transfer medium "Maintain water in the pipes with the help of a pump and thus created a forced circulation of the "water. "" "■" '' "■ ·

■ - ^ ORIGINAL INSPECTED CX) PY.

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Claims (8)

HOECHST AKTIENGESELLSCHAFT HOE 80 / H 021. Process for the production of phosphorus pentoxide using the heat of reaction Patent claims 1) Process for the production of phosphorus pentoxide by burning elemental phosphorus with the aid of air using the heat of reaction to generate energy, characterized in that the phosphorus combustion is carried out with dried air with a water content of 5 to 0.01 g / nr air in a combustion chamber , the metallic walls of which are formed into a cooling system having cavities, where in the cooling system a liquid or a liquid-vapor mixture suitable as a heat transfer medium for the heat of reaction ■ heated to temperatures of over 150 - 500 ° C at pressures of 1 - 150 bär is circulated "; that the vapor produced in the cooling system is continuously withdrawn from the latter and replaced by an equivalent amount of fresh liquid, and that the hot PO ^ vapors escaping from the combustion chamber are condensed or processed into secondary products. 2) Method according to claim 1, characterized in that the circulating liquid is water. 3) Method according to claim 1 or 2, characterized in that the circulated liquid or the liquid-vapor mixture is heated to 200-400 ° C at pressures of 15-90 bar. ORfGINAL INSPECTED 4) Method according to claims 1-3 » characterized in that. that the dried air has a water content of 0.3 to 0.1 g / nr air. 5) Method according to claims 1-4, characterized in that the walls or the cooling system of the combustion chamber are made of stainless steel. .6) Method according to claims 1-5, characterized in that the walls of the combustion chamber or the cooling system consists of a metallic pipe wall with directly welded pipes, a flow pipe wall or a membrane pipe wall. 1 ^ 7) Method according to claims 1-6, characterized in that the phosphorus pentoxide vapors leave the combustion chamber at a temperature of 300 to 1000 ° C. 8) Method according to claims 1-7, characterized in that the phosphorus pentoxide vapors escaping from the combustion chamber are further processed into phosphoric acid. COPY ORIGINAL INSPECTED